Here is the video:
Peter Hartman wrote:I am just curious about what you like or don't like about this design.
Here is the video:
I know it's been ages since you asked this, and it looks like Ernie missed it.
I personally like that geoff lawton design very much.
This design is one of the few I can imagine could be built by relatively handy permies with manageable risks, and the sort of 'on-demand' hot water that most people look for when they wax nostalgic about civilized comforts. It's not a "no-brainer" either for design, building, operation, or maintenance, but it handles some tricky problems in simple and clever ways.
I really like Geoff's presentation of it, too; he's a very good teacher.
He does gloss over some of the details.
- how to install waterproof, heat-resistant fittings onto a drum (this is a known art, but not necessarily a common skill that everyone has);
- galvanic corrosion and proper materials for compatible tank, coils, etc.
- what sorts of supports are needed to keep these layers of material in place; a water tank is heavy, and there's also thermal expansion tolerance needed.
- insulation needed for firebox and outer shell, to concentrate the heat under the tank. "Standard fireproof insulation" which he mentions is important for efficiency, but that will vary a bit in different regions. Roxul or rock wool might be good; fiberglass might be OK but might melt; ceramic-fiber would be good but expensive; vermiculite or perlite might work if you could contain it effectively and top up after settling.
- what length of flame path prevents creosote buildup on the tank, or how you clean it once creosote does build up.
- chimney design if building under a shelter or inside a house
- exactly how you top up, and how you know when it's needed
- how to size and arrange outlets, safety valves, etc. to avoid steam explosions and damage. He gets across the importance of this point nicely, just not the details.
- the relationship between pressurized and non-pressurized water in this system;
- system tolerances for water quality (filtered, alkalinity vs acid, etc), and any risks if water is contaminated or capable of clogging system.
- risks of maintaining a tank of water at warm temperatures over time.
This design brilliantly separates the clean, on-demand hot water in the coil from any gunge building up in the tank, and the tank protects that on-demand water from overheating while getting it to temperature quickly. He does mention the need to keep the tank topped up; this is a critical safety feature as well as functional consideration. If the coil is clean and only used for potable water, could potentially be used as a potable hot-water generator e.g. make a tea-tap on the side as well as sending it off to the showers.
Points of difference:
I do agree that sticks are easier to burn fast and clean; but I recognize that not everyone is on the small-fuels bandwagon yet.
We routinely use modest cordwood or moderate-sized logs in our rocket heater.
A taller firebox is needed to burn larger fuels cleanly, since any unburned fuels / remaining flames that contact that water tank will deposit creosote.
I love burning stick fuels for sustainability reasons as well as clean fire, plus they're easier and safer to harvest than timber. Dry faster too. Lumber scrap from projects also works, it doesn't have to be branches or pine cones.
Very dry fuel is as critical for clean fire, or more so.
The smokeless exhaust is a definite point in favor of this heater. I think he's in a hot, dry climate in Australia, so specifying small fuels is more of an issue than dry fuels. I'd want a dedicated woodshed nearby, with a raised floor to keep fuels above that steam drainage.
My understanding is that later, some people came along and plastered the whole thing in so it looks like a giant water-tower. At least I think that's the same system. Kinda fun to look at, but very hard to get at for maintenance, repairs, or remodels. With big home-built appliances like this, a 'steam-punk' aesthetic where you can see all the working parts is a plus for maintenance and early warning of repairs. Rather than encasing it in plaster or marble, I'd love to see one with stainless steel, or copper and brass detailing, exposed like a samovar.
Indoor construction option:
I would give this clever beast its own stall out back of an outdoor shower. I'd want more attention to safeties, chimney design, and excellent floor drains before I'd want it in a house with me.
He mentions the need to keep the tank topped up, but the method isn't shown - just a valve. Perhaps that valve is part of the pressurized system and that's why it spits out a lot of steam while it's open.
There's no discussion of 'gunge' buildup (mineral scale, biota growing if the tank is left lukewarm too long, etc) or how to remove it.
The black soot and gunk in the smoke chamber will need to be cleaned out periodically, though perhaps not for several years.
I would hope that at one end or the other, there's a large removable end or lid. I think being able to pull a bung off the tank and hose it out with cold water (shocking the scale off the outside of the pipes and hopefully the inside of the coil) would extend the maintenance life a bit.
Don't know how thick the tank is, whether it's enameled, whether it's a converted commercial tank or a home-built steel drum. A thick or enameled, or stainless, tank inside there would last a lot longer than a repurposed barrel.
If using a barrel, I'd probably leave the paint on except as needed for clean welds; the water inside should keep the temperature near the boiling point of water, and most industrial drums and water-heater enamels can take those temps and it would offer some protection from corrosion. But a tank upgrade is going to be cheap compared with the added years of use from it; you don't put this kind of system together for a weekend camping trip.
- Exaggeration / time delay of fire - I may have missed a time-lapse flame shot, but he didn't bring a big tank up to boiling on a handful of pine cones.
My guess is the tank's kept warm most of the time by that excellent insulation, and the fire just brought it back up to top heat.
- Steaming hot tap water is lovely if you know how to mix it down, but might not be safe for kids or folks with forgetfulness problems. If you can get an off-grid, thermostatically controlled mixing valve, that does not require electricity (a bimetal valve or something), that would be awesome. A small solar-powered thermostat and mixing valve could also be a nice addition.
It pays to have an experienced hot water tech involved when contemplating such a project. We heard from a fellow who helped with this system a few years ago, it wasn't just Geoff or generalist students who put it together. I was impressed with his general knowledge and trades experience; wish I could remember the name, or the details of his background that helped make this system a success on the first prototype.
Relevant experience can come from a range of backgrounds: plumbing, boiler mechanics, steam-fitters, HVAC guys who have worked with radiant floors or steam radiator systems.
Anyone with experience doing other off-grid plumbing projects like solar hot water will have a definite leg up on the problem solving, supplies, tools, and techniques. Making a couple regular rocket cookstoves or mass heaters before you try the combo system would be nice too.
There are just so many little details to manage, like how to protect pipes from freezing, scale, and fire; and of course pressure relief and drainage. Getting the right insulation, and sealing up the things that need to be sealed with good technique and materials, are all going to make things work better.
Here's one of the few threads where Ernie responded to some hot water questions directly: rocket-stove-water-heater thread. I think I like this design of Geoff's better than the one Ernie describes in the other thread, in general... but Ernie's would be easier to integrate into our standard rocket mass heater without altering the firebox or adding supports for the tall weight of a tank.
Geoff Lawton has a mechanical engineering background, and had Tim Barker's help with the original construction. Someone named Craig posted the details, and may be involved with ongoing info on the system.
As far as whose design it is: neither Tim nor Geoff seem particularly fussed about who gets the credit; they both worked on it. I don't think it's possible for two mechanically-oriented people to work on such a design together without collaboration; without anticipating and avoiding a few extra flaws because there were two informed minds giving their best to the project.
Peter Hartman wrote:Thanks Erica. This gives me some more to chew on before I jump into a similar project. It seems that filling the barrel with some sort of RV antifreeze could be beneficial to keep things from freezing or gunking up.
They top off the tank weekly or so using the same pressurized water that feeds the copper tubing for the heated water leading to the showers so using some sort of antifreeze would be tricky. For those of us that have freezing temps, I wouldn't think it would be necessary as long as you're there all the time. If going on a trip where you'll be gone for a few days, then you would want to drain the system so having drains at all the low spots would be necessary. Something they also do with RVs.
The other issue would be: Would that RV antifreeze raise the boiling point of the water? Probably. If so, then the straight water in the copper tubing could get above boiling temp causing a dangerous situation.
I've been looking for a good way to heat water and this looks like the ticket. The only thing I've come up with until now is a small elec water heater with shell and insulation stripped off, sitting half way on the back of our wood stove. I started out with just the tank, unplumbed but filled. That way no chance of pressure build up from potential boiling. Once comfortable with that, I plumbed it in. Problem is, we only have hot water in cold weather when the stove is going unless I run the elec element with the generator which takes a lot of fuel for a little hot water. 12 gal tank.
Geoff does mention that it's a stainless steel tank they used which is the high dollar lifetime guarantee water heaters here in the States. Hard to find used.
Now my dilemma is whether or not I should try this with my little 12 gal tank. I'm sure it would be enough to do some dishes but not sure if it would handle a shower. Past experience tells me we CAN take a shower with as little as 5 gal of water so it might do it. Really depends on the temp of the incoming water. I'll keep an eye out for a bigger tank though.
I can just see my neighbor stopping by while I'm working on this. He's been trying to convince me to make a still for corn liquor. LOL
NOTE* The 44 gal outer tank Geoff specs is 44 imperial gallons which is 55 US gal or 200 liters